1. Field of the Invention
The present invention relates to spinal fixation systems and methods, more specifically, a spinal fixation system that provides retention of a fixation rod wherein lateral and rotational movement of a fixation rod and bone fixation element are significantly reduced.
2. Description of Related Art
Spinal fixation, also referred to as vertebral fixation, is a neurosurgical procedure for reducing movement of a spine so as to decrease damage to the spinal cord and/or spinal roots. Spinal fixation is utilized to treat a wide variety of spinal disorders and deformities which result in vertebral displacement of the spine, including, but not limited to, scoliosis, kyphosis, spondylolisthesis, rotation, tumor diseases, disc degeneration, and congenital defects. In addition, spinal fixation is utilized to treat vertebral fractures, injuries, or other traumas to the spine wherein the spine becomes displaced from such fracture, injury, or trauma.
The procedure utilizes synthetic devices to anchor two or more vertebrae to one another in the spinal column. Such devices may include bone fixation elements, also referred to as bone screws, coupled to a spinal fixation rod via a coupling element. The bone fixation elements are inserted into the pedicle(s) of the desired vertebrae and are secured to or within the coupling element. The spinal fixation rod, in turn, is secured within the coupling element via a securing element. Accordingly, the spinal fixation rod is ultimately secured to the vertebrae such that movement of the stabilized vertebrae is limited. As the ultimate goal of spinal fixation is to limit movement of the spine, it is of great importance that fixation between the bone fixation element, coupling element, and fixation rod be rigid and permanent.
Various structures for securing the fixation rod within the coupling element are currently available. One such structure includes the use of a compression means, such as a compression screw, which exerts a predetermined amount of force on the fixation rod when the compression means is secured within the coupling element. Such compressive force also translates to a compressive force being applied on the coupling element and the bone fixation element as well, thereby reducing movement of the synthetic devices within the vertebra to which such synthetic devices are secured.
However, some synthetic devices require the bone fixation element to be secured within the coupling element at a substantially 90 degree angle thereto, thereby resulting in a substantially 90 degree insertion of the bone fixation element into the pedicle. Thus, use of such synthetic devices limits the ability to secure such devices at an angle customized to a patient, even if a more accurate and secure fixation would result if the bone fixation element were inserted into the pedicle at either an acute or obtuse angle. As such, there exists a need for an improved spinal fixation system that would permit rotational movement of a bone fixation element within the coupling element prior to insertion into a pedicle, but prevent movement thereof after insertion into the pedicle.
Moreover, although the compression means utilized in some synthetic devices results in a reduction of movement of the fixation rod within the coupling element, rotational movement of the fixation rod therein does not always result, as in some cases the compression means is not shaped so as to maximize the surface area contact between the compression means and the fixation rod. As such, there exists a need for an improved spinal fixation system that would limit both lateral and rotational movement of a fixation rod located within a coupling element.
Furthermore, some synthetic devices utilizing compression means may become loose over time due to vibrational forces applied thereto, thereby resulting in pain and discomfort in the patient and a need to perform corrective surgical procedures to re-tighten and re-secure the synthetic devices. As such, there exists a need for an improved spinal fixation system which would limit loosening of the synthetic devices due to vibrational forces.